Field of the Invention
The present invention relates to a plastics composition pigmented with platelet-shaped metal pigments, a method for production of same and use thereof.
Surfaces which are dyed or coated dark for esthetic or technical reasons and are exposed to sunlight have the usually undesired property of heating up to a greater or lesser extent depending on the color depth. The solar heating of dark surfaces is perceived as extremely unpleasant for example in vehicle interiors. Dark surfaces heat up to a greater or lesser extent as a function of solar absorption and dissipate this absorbed heat as heat radiation and via air convection for example into the interior of a vehicle. Furthermore, the relatively high heat storage capacity of these dark surfaces contributes to the heating for example of vehicle interiors. The higher the thermal capacity and thermal conduction into the material, the more solar energy that can be stored in the materials. The heat dissipation then takes place slowly via heat radiation and convectively via the air.
Description of Related Art
WO 02/12405 A2 relates to a flat element having a dark surface and exhibiting a reduced solar absorption, wherein the reflectance of the substrate of the flat element is less than 50% in the visible light range of from 380 to 720 nm and more than 60% in the near-infrared range of from 720 to 1500 nm. The coating of the substrate consists of a binder which has a transparency greater than 70% in the spectral range of from 380 to 1500 nm and first pigments which give the coating a reflectance of less than 50% in the visible light range and give the coating a transparency of more than 50% in the near-infrared spectral range and/or second pigments which give the coating a reflectance of less than 50% in the visible light range and give the coating a reflectance of more than 40% in the near-infrared spectral range. The first pigments are organic pigments which are used in a quantity of from 0.2 to 20 wt.-%, in relation to the total formulation, to produce the coating. The second pigments are inorganic pigments, such as e.g. coated, platelet-shaped mica pigments which are used in a quantity of from 4 to 50 wt.-%, in relation to the total formulation, to produce the coating. The flat element has a high reflectance in the near-infrared range in order, despite the dark dyeing in the visible range, to reduce the heating under sunlight, which is desired in applications which are not to heat up under sunlight even though they have dark surfaces. No metal effect pigments are used for the pigmentation.
A dark, flat element with low solar absorption, i.e. a combination of a carrier material with components embedded therein, is also claimed in WO 2006/058782 A1. The element has an average reflectance of less than 50% in the visible light wavelength range of from 400 to 700 nm; the average reflectance in the near-infrared wavelength range of from 700 to 1000 nm is more than 50%. The carrier material can be a plastic. The embedded components include, among other things, pigments, but not metal pigments, and dyes.
WO 00/24833 A1 discloses a coating with spectral selectivity, in particular for deposit surfaces in motor vehicles, comprising a) a binder with a transmittance of 60% or more in the near-infrared wavelength range of from 0.7 to 2.5 μm, and with a transmittance of 40% or more in the thermal infrared wavelength range, b) first pigments which absorb 40% or more of the visible light in the wavelength range of from 0.35 to 0.7 μm, have a backscatter of 40% or more in the near-infrared of from 0.7 to 2.5 μm and have an absorption of 60% or less in the thermal infrared wavelength range, c) second pigments which have a backscatter and/or reflectance of 40% or more in the thermal infrared wavelength range. The binder can here be selected from thermoplastic materials such as polyolefins and polyvinyl compounds. The first pigments can be inorganic or organic pigments. The second pigments include, among other things, platelet-shaped metals or metal alloys, such as iron for example.
A coating with low solar absorption is disclosed in WO 02/057374 A1. This coating comprises a) a binder and/or a binder combination, b) first pigments which have a transparency greater than 70% in the wavelength range of from 300 to 2500 nm, the particle size of which is chosen such that they have a high backscatter greater than 70% in the near-infrared wavelength range of from 700 to 1500 nm and which have an absorption greater than 40% in the thermal infrared range of from 5 to 50 μm, c) second pigments which absorb spectral-selectively in the visible light wavelength range of from 400 to 700 nm and/or more than 50% in the entire visible light wavelength range, which have a transparency greater than 50% in the near-infrared wavelength range of from 70 to 1500 nm and which have an absorption greater than 40% in the thermal infrared range, and/or d) third pigments which absorb spectral-selectively in the visible light spectral range and/or absorb more than 50% in the entire visible light wavelength range and which are reflective with a reflectance greater than 50% in the near-infrared spectral range and which have an absorption greater than 40% in the thermal infrared range, e) fillers. The first and third pigments can be inorganic pigments, the second pigments are organic pigments, metal pigments are not mentioned.
DE 25 44 245 A1 mentions the possibility of incorporating IR-reflective pigments into molding materials, wherein the pigments align largely surface parallel during processing. According to EP 1 256 437 A1, however, the alignment of the particles is not as good in a plastic body made of e.g. extruded molding material with IR-reflective pigments distributed uniformly therein as in the case of a coextruded or varnished separate layer. According to EP 1 256 437 A1 this applies in particular to plastic bodies with a comparatively complicated geometry, which deviate from the simple plate shape and in the production of which different melt flow directions and shear forces occur during the extrusion, which force the pigment particles into different alignments and thus also expose them to higher mechanical stresses overall.
EP 1 256 437 A1 relates to a method for producing a light-permeable, IR-reflective plastic body, consisting entirely or at least partially of an impact-resistant thermoplastic, containing 0.01 to 5 wt.-% reflective particles made of platelet-shaped carrier pigments coated with a metal oxide.
DE 100 10 538 A1 describes a dirt-repellent coating material with spectral-selective properties which comprises, among other things, a binder with good UV resistance and first, platelet-shaped particles. The latter reflect in the thermal infrared wavelength range of from 5 to 100 μm. The first platelet-shaped particles can be for example metals and/or metal alloys of aluminum, aluminum bronze, iron, copper, zinc or tin. The binders can be selected e.g. from thermoplastic materials such as polyolefins or polyvinyl compounds.
EP 0 673 980 A2 relates to colored iron or iron alloy pigments which are obtained at an elevated temperature in an oxygen-containing atmosphere. These pigments can be used for example in plastics in order to imitate a granite effect.
EP 1 541 636 A1 describes a thermoplastic plastics composition which comprises 0.1 to 15 parts by mass of inorganic pigment with infrared-reflective properties. The inorganic pigment can contain at least one of the elements Fe, Cr, Mn, Cu, Co or Ni and can be selected for example from the oxides FeO, FeO(OH), Fe2O3, CrO, Cr2O3, MnO or CuO.
EP 1 916 352 A2 discloses a roofing product which comprises two coextruded polymer layers, wherein the first layer reflects in the near-infrared and the second layer is permeable in that range. Both layers can be pigmented, wherein metal pigments or metal platelets encapsulated in silicon dioxide can be used as solar-reflective pigments.
WO 2012/075369 A1 discloses compositions which are used to form products with an increased reflectance in the near-infrared range. Metals or metal alloys of e.g. aluminum, cobalt, iron, manganese or zinc can be used as infrared-reflective pigments.
CN 102627828 A claims a plastics composition which contains 0.1 to 2.0 parts by weight metal pigment, 0.1 to 2.0 parts by weight infrared-reflective pigment, 0.1 to 2.0 parts by weight lubricant, 0.1 to 1.0 parts by weight antioxidant, 0.1 to 0.5 parts by weight toner. Aluminum or silver powder, among other things, can be used as metal pigment; iron, copper or zinc, for example, can be used as infrared-reflective pigment.
US 2008/0138609 A1 discloses a plastics composition which comprises less than 5 wt.-% infrared-reflective pigments. An inorganic color pigment, such as described e.g. in U.S. Pat. No. 6,036,763 A or U.S. Pat. No. 6,174,360 B1, is used as infrared-reflective pigment.